The invention relates to apparatus for damping vibrations, especially torsional vibrations between the output element (e.g., a crankshaft) of an engine and the power train in a motor vehicle. More particularly, the invention relates to improvements in apparatus of the type having at least two flywheels which are rotatable relative to each other against the opposition of damper means wherein one flywheel is the input member and the other flywheel is the output member of the damper means. The output member can be coupled to the power train by a clutch, particularly a friction clutch.
Heretofore known vibration damping apparatus of the above outlined type employ dampers which have energy storing elements acting in the circumferential direction of the flywheels and normally including coil springs which store elastic energy, and additional energy storing elements which act in the axial direction of the flywheels and cooperate with friction pads and/or linings to produce friction (i.e., hysteresis). The means for generating friction operate in parallel with energy storing means which act in the circumferential direction of the flywheels.
It has been found that certain conventional vibration damping apparatus can operate satisfactorily (i.e., they are capable of damping torsional vibrations as well as noise) but only under specific circumstances. Thus, the mode of operation of such conventional apparatus is not entirely satisfactory under many operating conditions because their design is a compromise due to an attempt to ensure satisfactory or acceptable operation under a variety of different conditions. For example, a purely mechanical solution does not suffice to cover a wide spectrum of operating conditions entailing the development of many basically different stray movements and noise levels. Moreover, purely mechanical solutions are quite expensive, especially if they are to adequately suppress stray movements and noise under a variety of different operating conditions. This is due to the fact that, if a mechanically operated vibration damping apparatus is to counteract a wide range of amplitudes of undesirable stray movements of the flywheels relative to each other, such undertaking greatly increases the cost, bulk, complexity and sensitivity of the apparatus. Moreover, even a very complex and expensive mechanical vibration damping apparatus is incapable of operating satisfactorily under any one of a wide range of different operating conditions because the individual damper stages (i.e., hystereses produced by individual energy storing elements which act in the circumferential direction of the flywheels) cannot be altered as a function of changes in operating conditions. Still further, presently known apparatus are subject to extensive wear so that their useful life is relatively short, and they are also prone to malfunction.